In the conventional manually operated ink stamp, a printing die, which is impregnated with ink, is mounted on the lower surface of a die holder contained within an outer housing or base. A stem connected to the upper surface of the die holder projects upwardly through an opening in the base and carries a handle. The die holder is biased to a raised position, in which the die is located out of contact with the material to be printed, by a compression spring which is positioned around the stem and is interposed between the base and the handle. By applying a manual force to the upper end of the handle, the spring force will be overcome to move the die downwardly into contact with the material to be printed.
When using ink stamps having a microporous die preimpregnated with ink, proper control of the stamping pressure is critical. If the stamping pressure is too great, an unnecessarily large quantity of ink will be expelled from the die and the printing impression may be overly dark or smudged. On the other hand, if the stamping pressure is too light, an insufficient quantity of ink will be discharged from the die and the printing impression will be light and illegible.
In the past, various attempts have been made to provide an adjustment for the stamping pressure. In one such device, as illustrated in U.S. Pat. No. 4,022,127, a two part bushing is located below the handle and acts as a stop to limit vertical depression of the handle. By threaded adjustment of the bushing, the position of the stop can be varied to thereby vary the distance which the handle may be depressed.
U.S. Pat. No. 4,203,362, also shows an adjusting mechanism which will limit the stroke of travel of the handle to thereby vary the printing impression.
In the U.S. Pat. No. 4,362,101, an adjusting mechanism is provided which will adjust the position of the die holder and the die relative to the base or housing. By varying the position of the die within the base, the printing impression can be controlled.
With any ink stamp, there are certain areas on the die which are blank or free of printing. If a heavy or excessive force is applied to the handle, these non-printing areas can contact the paper or other material to be printed, leaving a smudge on the paper. Because of this, it has been the practice to seal the non-printing areas on the die by applying a plastic coating to these areas. As the sealing operation is done manually, it is time consuming and increases the overall cost of the stamp.